BCSE Pharmacology

Endocrine Drugs – BCSE Study Guide

March 28, 2026 30 min read 31 views

Endocrine pharmacology is essential for BCSE success, covering drugs that treat some of the most common conditions in veterinary practice.

Overview and Clinical Importance

Endocrine pharmacology is essential for BCSE success, covering drugs that treat some of the most common conditions in veterinary practice. This guide covers four major drug categories: insulin and oral hypoglycemics for diabetes management, thyroid drugs for hypo- and hyperthyroidism, corticosteroids for inflammation and immune suppression, and reproductive hormones for breeding management and pregnancy control. Understanding species differences in drug metabolism and clinical applications is crucial for exam success.

High-YieldEndocrine drugs appear frequently in BCSE questions due to the high prevalence of diabetes, thyroid disease, and the widespread use of corticosteroids. Pay special attention to species-specific dosing, especially the key difference between prednisone and prednisolone in cats.

Insulin Type	Onset (hr)	Peak (hr)	Duration (hr)	Species Use
Regular (Crystalline)	0.5-1.5	2-4	4-6	DKA emergencies
NPH (Humulin N)	1-2	4-8	8-14	Dogs (1st line)
Lente (Vetsulin)	1-2	4-10	8-14	Dogs (FDA approved)
PZI (ProZinc)	1-3	5-7	8-24	Cats and Dogs (FDA approved)
Glargine (Lantus)	2-4	No peak	12-24	Cats (high remission)
Detemir (Levemir)	2-4	No peak	12-24+	Cats and Dogs (potent)

Drug	Mechanism	Dose	Notes
Glipizide	Sulfonylurea - stimulates pancreatic beta cell insulin secretion	2.5 mg/cat PO q12h	Cats only. Requires functional beta cells.
Acarbose	Alpha-glucosidase inhibitor - delays intestinal glucose absorption	12.5-25 mg/animal PO with meals	Adjunctive. GI side effects common.
Velagliflozin (Senvelgo)	SGLT2 inhibitor - increases renal glucose excretion	1 mg/kg PO once daily	FDA approved for cats. NOT for insulin-treated cats.

Section 1: Insulin and Oral Hypoglycemics

Diabetes Mellitus Overview

Diabetes mellitus is a common endocrine disease in dogs and cats characterized by persistent hyperglycemia due to relative or absolute insulin deficiency. Dogs typically develop Type 1 (insulin-dependent) diabetes requiring lifelong insulin therapy. Cats more commonly develop Type 2 (non-insulin-dependent) diabetes and may achieve remission with appropriate treatment. Clinical signs include polyuria, polydipsia, polyphagia, and weight loss.

MEMORY AID - The 4 Ps of Diabetes

Polyuria, Polydipsia, Polyphagia, and (weight) Plummeting - these are the classic signs of uncontrolled diabetes mellitus in dogs and cats.

Insulin Types and Classification

Insulin preparations are classified by their duration of action. Understanding onset, peak, and duration is essential for proper diabetic management and recognizing when hypoglycemia is most likely to occur.

High-YieldProZinc (PZI) is FDA-approved for BOTH dogs and cats. Vetsulin (Lente) is FDA-approved for dogs. Glargine achieves the highest diabetic remission rates in cats but is NOT FDA-approved for veterinary use.

MEMORY AID - Insulin Concentration Matching

"Vet-40, Human-100" - Vetsulin and ProZinc are U-40 concentrations (use U-40 syringes). Human insulins (NPH, Glargine, Detemir) are U-100 (use U-100 syringes). NEVER mix syringes - this is a common cause of dosing errors!

Species-Specific Insulin Protocols

DOGS: Start with NPH or Lente (Vetsulin) at 0.25-0.5 U/kg SC every 12 hours. Most dogs require twice-daily dosing. Adjust doses no more frequently than every 1-2 weeks based on glucose curves.

CATS: Glargine or PZI are preferred for their longer duration and higher remission potential. Starting dose: 1-2 U/cat (or 0.25-0.5 U/kg) SC every 12 hours. Combine with high-protein, low-carbohydrate diet. Up to 50% of cats may achieve diabetic remission with appropriate management.

Oral Hypoglycemic Agents

Oral hypoglycemics have limited use in veterinary medicine because dogs are typically insulin-dependent. They may be used in cats with mild diabetes or as adjunctive therapy.

High-YieldVelagliflozin (Senvelgo) is a newer SGLT2 inhibitor FDA-approved for cats not previously treated with insulin. It is CONTRAINDICATED in cats with prior insulin use, DKA history, or concurrent renal/hepatic disease.

MEMORY AID - SGLT2 Inhibitors

"Sugar Gets Lost Through 2 kidneys" - SGLT2 inhibitors work by preventing glucose reabsorption in the kidneys, causing glucosuria (glucose in urine). This is the desired effect, not a side effect!

Hypoglycemia: Recognition and Treatment

Clinical signs of hypoglycemia include: weakness, lethargy, trembling, incoordination, seizures, blindness, behavior changes, and coma. Most common causes include insulin overdose, missed meals, or increased activity.

Emergency Treatment: If conscious - rub corn syrup or sugar water on gums and offer food. If collapsed - apply corn syrup to gums (do NOT force fluids into mouth). Severe cases - 50% dextrose 0.5-1 mL/kg IV diluted 1:4, given slowly over 10 minutes.

MEMORY AID - Hypoglycemia Signs - "WHATS Wrong"

Weakness, Hunger, Anxiety/restlessness, Trembling, Seizures - these signs indicate hypoglycemia. Always have corn syrup available for diabetic patients!

Parameter	Levothyroxine (Thyro-Tabs, Soloxine)
Mechanism	Synthetic T4 replacement - converted to active T3 in peripheral tissues
Dog Dose	0.02 mg/kg (22 mcg/kg) PO every 12 hours. Base dose on lean body weight in obese patients.
Cat Dose	Rare use - typically for iatrogenic hypothyroidism post-radioiodine or thyroidectomy. Start low.
Administration	Give on empty stomach for best absorption. Give consistently with or without food.
Monitoring	Check T4 at 4-6 hours post-pill (peak) after 4 weeks of therapy. Target: upper half of reference range.
Response Time	Energy improves in 1-2 weeks. Skin/coat may take 2-3 months to fully resolve.

Parameter	Methimazole (Tapazole, Felimazole)
Mechanism	Thioureylene antithyroid drug - blocks thyroid peroxidase enzyme, inhibiting T4/T3 synthesis
Cat Dose	Start: 1.25-2.5 mg/cat PO or transdermal every 12 hours. Titrate to maintain T4 1.0-2.5 mcg/dL.
Formulations	Oral tablet, liquid, or transdermal gel (applied to inner ear pinna). Transdermal may reduce GI side effects.
Onset	Clinical improvement in 3-4 weeks. T4 decreases within 1-2 weeks.
Side Effects	GI upset (vomiting, anorexia), facial excoriation, bone marrow suppression (rare but serious), hepatotoxicity
Monitoring	CBC, chemistry, T4 every 2 weeks for first 3 months. Then every 3-6 months. Watch for UNMASKING of renal disease.

Section 2: Thyroid Drugs

Thyroid Physiology Review

The hypothalamic-pituitary-thyroid axis regulates metabolism. The hypothalamus releases TRH (thyrotropin-releasing hormone), which stimulates the pituitary to release TSH (thyroid-stimulating hormone). TSH stimulates the thyroid gland to produce and release T4 (thyroxine) and T3 (triiodothyronine). T4 is the main circulating form and is converted to the active T3 in peripheral tissues. Negative feedback from T4/T3 inhibits TRH and TSH release.

MEMORY AID - HPT Axis Flow

"TRH Tells TSH to Tell Thyroid" - Remember the cascade: Hypothalamus (TRH) leads to Pituitary (TSH) leads to Thyroid (T4/T3). T4 is "Four" - four iodine atoms. T3 is "Three" - three iodine atoms and the active form.

Hypothyroidism Treatment: Levothyroxine

Hypothyroidism is common in dogs (rare in cats except iatrogenically after hyperthyroid treatment). It results from destruction of the thyroid gland, most often from lymphocytic thyroiditis or idiopathic atrophy. Clinical signs include obesity, lethargy, cold intolerance, bilaterally symmetric alopecia, bradycardia, and skin changes.

High-YieldLevothyroxine doses in dogs are MUCH HIGHER than in humans due to shorter half-life and faster metabolism. The dog dose (22 mcg/kg) is roughly 10x higher per kg than the typical human dose.

MEMORY AID - Levothyroxine = T4

"Levo-T4-roxine" - Levothyroxine IS T4. The body converts it to active T3. Dogs need higher doses than humans because they metabolize it faster.

Hyperthyroidism Treatment: Methimazole

Hyperthyroidism is the most common endocrine disorder in middle-aged to older cats (greater than 7 years). It is caused by functional thyroid adenoma or adenomatous hyperplasia in approximately 97% of cases; thyroid carcinoma is rare in cats but is the primary cause in dogs. Clinical signs include weight loss despite increased appetite, hyperactivity, vomiting, diarrhea, tachycardia, and palpable thyroid nodule.

High-YieldTreating hyperthyroidism in cats can UNMASK underlying renal disease. The hyperthyroid state increases GFR, making kidney function appear better than it truly is. Always monitor renal values after initiating treatment!

MEMORY AID - Methimazole Side Effects - "VBLS"

Vomiting, Blood dyscrasias (bone marrow), Liver toxicity, Scratching (facial excoriation) - monitor CBC and chemistry in the first 3 months when side effects are most likely!

Treatment Options Comparison for Feline Hyperthyroidism

MEMORY AID - Radioiodine = CURE

"I-131 = 1 treatment, 3-4 weeks isolation, 1 cure" - Radioiodine therapy is the CURATIVE treatment of choice for feline hyperthyroidism because it selectively destroys hyperfunctional thyroid tissue.

Treatment	Advantages	Disadvantages	Best Candidates
Methimazole	Reversible, affordable, widely available, can assess kidney function	Lifelong daily dosing, side effects, does not stop tumor growth	All cats initially. Long-term for those with renal concerns.
Radioiodine (I-131)	Curative, single treatment, no anesthesia, no daily medication	Requires hospitalization at licensed facility, expensive, risk of hypothyroidism	Cats with normal renal function and no contraindications.
Thyroidectomy	Curative, immediate effect	Anesthesia risk, potential parathyroid damage causing hypocalcemia	Unilateral disease, when I-131 unavailable.
Iodine-restricted diet	No medication needed	Must be ONLY food consumed, may not adequately control all cats	Cats that cannot receive other treatments.

Drug	GC Potency	MC Potency	Duration	Half-life	Equivalent Dose
Hydrocortisone (Cortisol)	1	1	Short (8-12 hr)	1.5 hr	20 mg
Prednisone/Prednisolone	4	0.8	Intermediate (12-36 hr)	2.5 hr	5 mg
Methylprednisolone	5	0.5	Intermediate (12-36 hr)	3.5 hr	4 mg
Triamcinolone	5	0	Intermediate (12-36 hr)	3-5 hr	4 mg
Dexamethasone	25-30	0	Long (36-72 hr)	36-54 hr	0.75 mg
Betamethasone	25-30	0	Long (36-72 hr)	36-54 hr	0.6 mg

Section 3: Corticosteroids

Corticosteroid Classification and Physiology

Corticosteroids are hormones produced by the adrenal cortex or synthetic analogs. They are divided into glucocorticoids (affecting glucose metabolism, inflammation, and immunity) and mineralocorticoids (affecting electrolyte and water balance). Most therapeutic corticosteroids are glucocorticoids. The HPA (hypothalamic-pituitary-adrenal) axis regulates endogenous cortisol production through negative feedback.

Mechanism of Action

Glucocorticoids bind to intracellular receptors and alter gene transcription. Anti-inflammatory effects include: inhibition of phospholipase A2 (blocking arachidonic acid release), decreased production of prostaglandins, leukotrienes, and cytokines, stabilization of cell membranes, reduction of capillary permeability, and inhibition of leukocyte migration.

MEMORY AID - Glucocorticoid Actions - "SLIM PIG"

Suppresses inflammation, Lymphocyte reduction, Immunosuppression, Metabolic effects (glucose up), Polyuria/Polydipsia, Inhibits phospholipase A2, Gluconeogenesis increased

Glucocorticoid Comparison

GC = Glucocorticoid, MC = Mineralocorticoid. Relative potencies compared to hydrocortisone (=1).

High-YieldCATS CANNOT CONVERT PREDNISONE TO PREDNISOLONE efficiently - always use PREDNISOLONE in cats. Horses also have poor prednisone conversion. Dexamethasone has NO mineralocorticoid activity, making it preferred when fluid retention is a concern.

MEMORY AID - Prednisone vs Prednisolone

"PrednisoNE Needs Enzyme" - Prednisone is a prodrug that requires hepatic conversion to active prednisolone. Cats and horses lack efficient conversion. Use prednisolONE directly in these species - it is already DONE being converted!

Clinical Dosing Guidelines

MEMORY AID - Steroid Dose Escalation

"0.5, 2, 4" - Anti-inflammatory starts around 0.5-1 mg/kg/day. Immunosuppressive is 2-4x higher. Cats need approximately DOUBLE the anti-inflammatory dose of dogs for comparable effect.

Side Effects and Iatrogenic Cushing's

Short-term side effects: Polyuria, polydipsia, polyphagia, panting (dogs), behavioral changes, GI upset

Long-term side effects (greater than 4 months): Iatrogenic Cushing's syndrome, muscle wasting, pot-bellied appearance, thin skin, alopecia, calcinosis cutis, hepatomegaly, delayed wound healing, increased susceptibility to infections (including UTI in up to 30% of patients)

HPA axis suppression: Prolonged steroid use suppresses ACTH release and causes adrenal atrophy. ALWAYS taper steroids gradually after extended use to prevent acute adrenal insufficiency.

High-YieldNEVER stop steroids abruptly after prolonged use! Gradual tapering over 2-4 weeks (or longer for extended therapy) is essential to allow HPA axis recovery and prevent potentially fatal adrenal crisis.

MEMORY AID - Steroid Side Effects - "3Ps and THRUST"

Polyuria, Polydipsia, Polyphagia + Thin skin, Hepatomegaly, Reduced immunity, UTIs common, Slow wound healing, Truncal obesity

Dose Category	Prednisolone Dose	Clinical Applications
Physiologic Replacement	0.2 mg/kg/day	Addison's disease (hypoadrenocorticism)
Anti-inflammatory (Dogs)	0.5-1 mg/kg/day (up to 2 mg/kg for severe)	Allergies, atopy, inflammatory conditions
Anti-inflammatory (Cats)	1-2 mg/kg/day	Asthma, inflammatory bowel disease, allergies
Immunosuppressive (Dogs)	2-4 mg/kg/day (up to 6.6 mg/kg)	IMHA, ITP, immune-mediated polyarthritis, pemphigus
Immunosuppressive (Cats)	4.4 mg/kg/day	Immune-mediated diseases

Drug	Mechanism/Use	Clinical Applications
Gonadorelin (GnRH)	Stimulates FSH and LH release from pituitary	Treatment of ovarian follicular cysts in cattle. Part of Ovsynch protocol for timed AI.
Deslorelin (GnRH agonist)	Initial stimulation then downregulation of GnRH receptors	Short-term: estrus induction in mares/bitches. Long-term: reversible contraception (suppression)
hCG (human chorionic gonadotropin)	LH-like activity - induces ovulation	Induction of ovulation in mares and induced ovulators (cats)
eCG/PMSG (equine chorionic gonadotropin)	FSH-like activity - stimulates follicular development	Superovulation protocols, estrus induction in anestrous animals

Section 4: Reproductive Hormones

Reproductive Endocrinology Overview

The hypothalamic-pituitary-gonadal axis controls reproduction. GnRH from the hypothalamus stimulates the pituitary to release FSH (follicle development, estrogen production) and LH (ovulation, corpus luteum formation). The corpus luteum produces progesterone to maintain pregnancy. Prostaglandin F2alpha from the uterus causes luteolysis (corpus luteum regression) when pregnancy does not occur.

MEMORY AID - HPG Axis

"GnRH Gets the LH and FSH Going" - GnRH from hypothalamus triggers FSH (Follicle growth) and LH (Luteinizing/ovulation) from the pituitary. Remember: FSH = Follicle, LH = Luteinizing.

GnRH and Gonadotropins

High-YieldThe Ovsynch protocol for timed AI in cattle: Day 0 - GnRH (100 mcg), Day 7 - PGF2alpha (25 mg), Day 9 - GnRH (100 mcg), then breed 0-20 hours after second GnRH. This allows breeding without estrus detection.

MEMORY AID - Ovsynch Protocol

"GnRH-7-PG-9-GnRH-Breed" - GnRH on Day 0, Prostaglandin on Day 7, GnRH on Day 9, then Breed. The numbers (0-7-9) are easy to remember!

Prostaglandins

Prostaglandin F2alpha (PGF2alpha) and its analogs are primarily used for their luteolytic (corpus luteum-destroying) effects. They also stimulate uterine contractions and may cause cervical dilation. These are essential drugs in food animal and equine reproductive management.

Prostaglandin Side Effects and Safety

Side effects by species: HORSES - sweating, abdominal discomfort (colic), increased respiratory rate. CATTLE - increased salivation, mild discomfort. DOGS/CATS - salivation, vomiting, diarrhea, restlessness, urination, hyperthermia. Side effects are typically transient (30-60 minutes).

HUMAN SAFETY WARNING: Prostaglandins are readily absorbed through skin. PREGNANT WOMEN and those of childbearing age should NOT handle these drugs. Can cause bronchospasm in asthmatics.

MEMORY AID - PGF Side Effects - "SCUD"

Salivation, Colic (horses), Uterine contractions, Diarrhea - these are the common transient side effects of prostaglandins. They resolve quickly.

High-YieldProstaglandins require a MATURE corpus luteum (at least 5 days post-ovulation) to work effectively. They will NOT cause luteolysis in early diestrus when the CL is not yet responsive.

Progestins and Progesterone

Progesterone and synthetic progestins mimic the luteal phase of the estrous cycle. They block the LH surge and prevent estrus by negative feedback on the hypothalamus and pituitary. They are used for estrus suppression, synchronization, and pregnancy maintenance.

High-YieldAltrenogest (Regu-Mate) is HAZARDOUS to humans and is absorbed through skin. Women of childbearing age should NEVER handle this product. Always wear gloves!

MEMORY AID - CIDR Protocol

"CIDR = Controlled Internal Drug Release" - Insert for 7 days with GnRH on Day 0, remove on Day 7 with PGF2alpha, then breed based on estrus detection or give GnRH for timed AI.

Pregnancy Termination Drugs

Various drugs can terminate pregnancy depending on species and gestational stage. The approach differs significantly between species due to differences in pregnancy maintenance.

MEMORY AID - Dog Pregnancy Maintenance

Dogs have ONLY LUTEAL progesterone throughout gestation - no placental progesterone. Therefore, anything that destroys the CL (prostaglandins) or blocks progesterone action (aglepristone) can terminate pregnancy at any stage.

Drug	Dose/Route	Clinical Uses
Dinoprost (Lutalyse)	Cattle: 25 mg IM. Mares: 5-10 mg IM. Dogs: 0.1-0.25 mg/kg SC BID-TID x 5-7 days	Estrus synchronization, pregnancy termination, pyometra treatment (with open cervix)
Cloprostenol (Estrumate)	Cattle: 500 mcg IM. Mares: 250 mcg IM	Estrus synchronization. More potent synthetic analog with fewer side effects.
Misoprostol (PGE1 analog)	Topical cervical application or oral	Cervical dilation for parturition induction, abortion. NOT luteolytic.

Drug	Route/Formulation	Primary Uses
Altrenogest (Regu-Mate)	Oral solution - 0.044 mg/kg PO daily (horses)	Mares: estrus suppression, synchronization, pregnancy maintenance. Gilts: estrus synchronization.
CIDR (progesterone)	Intravaginal device - 7 days	Cattle/sheep: estrus synchronization in cyclic and anestrous animals
Melengestrol acetate (MGA)	Feed additive - 0.5 mg/head/day for 14 days	Heifers: estrus suppression, synchronization, improved feed efficiency
Medroxyprogesterone (Depo-Provera)	Injectable - variable doses	Dogs/cats: estrus suppression, behavioral modification. CAUTION: significant side effects

Drug Class	Mechanism	Best Timing	Species Notes
Prostaglandins (PGF2alpha)	Luteolysis, uterine contraction	After Day 25-30 in dogs (easier later)	Primary method in horses, pigs. Dogs require multiple doses over days.
Aglepristone (Alizin)	Progesterone receptor antagonist - blocks P4 action	Up to Day 45 in dogs	Licensed in Europe. Effective in dogs. Not available in US.
Cabergoline	Dopamine agonist - inhibits prolactin which supports CL in mid-late pregnancy	After Day 40 in dogs	Often combined with PGF for better efficacy. Minimal side effects.
Corticosteroids + PGF2alpha	Mimics fetal cortisol signal, enhances luteolysis	Late gestation	Used in cattle and sheep for pregnancy termination and parturition induction.

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Endocrine Drugs &ndash; BCSE Study Guide